1. Technical Field
This application relates to the transmission of independent data signals over a communication link. In particular, this application relates to a method of transmitting a plurality of independent data signals from a transmitting module to a receiving module and to a transmitting and/or receiving apparatus connectable to a communication link, especially for use in communication networks provided on vehicles.
2. Related Art
Modern vehicles may include a number of information and entertainment components. Thus, vehicles may be provided with a high speed network as an infrastructure for managing the components in the vehicle that need to interact. As a standard for high speed multi media busses in vehicles, the MOST (Media Oriented Systems Transport) technology has found wide acceptance as a vehicle multi media bus. This bus allows a cost efficient communication between all functional blocks of entertainment and information systems, such as CD and DVD players, CD/DVD changers, cell phones, video systems, in-car PC's and the like. The network bus described by the MOST standard offers a speed of 24.8 Mbits/second which makes it about 100 times faster than the control-area network (MAY) busses. MAY busses are typically used in power train applications. The MOST specification defines the hardware interface needed to communicate over the bus. According to the MOST standard, either a plastic optical fiber or an electric wired connection may be employed for the physical bus.
An electric wired communication bus in a vehicle may be implemented in the form of a twisted pair connection. A twisted pair is a two lead wire usually made of copper that connects the different modules. In order to reduce cross talk or electromagnetic induction between pairs of wires, the two insulated wires are twisted around each other. Each connection of a twisted pair requires both wires. The twisted pair may either be used as a shielded twisted pair or as an unshielded twisted pair.
In a general configuration of a vehicle including a plurality of communication devices as part of an entertainment and information system, the communication devices installed on vehicle range from data generating devices, like radio or TV tuners or PCs, over data processing units (like amplifiers) and user interfaces to reproducing units such as displays and loud speakers. In the structure of the underlying communication system, a bus may be connected to the individual communication devices. The bus configuration may be a uni-directional data transmission. Alternatively, the data may be transmitted in a bi-directional manner between each or at least a sub-set of the communication devices connected to communication link.
In a general configuration of two modules or apparatus connected to an electrical MOST bus data may be transferred from a first module to a second module via communication link. The communication link may be implemented in the form of a twisted pair of cables. Data stemming from a data source of the transmitting module may be transferred on a symmetrical basis over a twisted pair of cable. In the receiving module, the data may be recovered by a data sink. In order to avoid any degradation of the data quality due to EMI (Electromagnetic Interference) the communication link may be decoupled from the data source and the data sink by providing transformers in-between. The transformers effect a complete galvanic decoupling of the internal processing within the modules from the signal on the cable. The signal is transmitted on the cable as a differential signal.
Additional data signals may be transmitted between a transmitting module and a receiving module by providing additional cables between both modules. Alternatively, independent data signals to be transmitted between both modules may be merged by modulating both signals and respectively demodulating the signals at the receiving side.
These systems for transmitting a plurality of independent data signals between interconnected modules result in additional hardware effort. A supplementary cable connection results in a duplication of the existing communication hardware. On the other hand, the use of modulation and demodulation stages results in an increased hardware and computation effort on the transmitting and receiving sides. Moreover, such additional processing steps generally do not allow maintenance of existing communication systems that are also affected by the additional processing stages.
Thus, there is a need for a method for transmitting a plurality of independent signals between modules connected to a communication link and corresponding apparatuses connectable to the communication link, where the transfer of an additional data signal may be achieved with less hardware/computational efforts.